Lenses of this kind have to be mass-produced at low cost with good accuracy by, for example, injection molding of a transparent optical resin. Besides, when used, a plurality of lenses are combined in many cases. The patent document 1 describes a configuration of an optical lens such as an objective lens in an optical pickup in which a mark is provided in an outer periphery to the lens effective radius part so as to be concentric with the lens effective radius part, which, for example, facilitates the alignment of axes of combined lenses. The document also describes a method in which a plurality of lenses are assembled by fitting projected and recessed portions on surfaces in an outer peripheral parts of lens effective radius parts, whereby the phase matching of the plurality of lenses is facilitated.
The Patent Document 2 describes a configuration of an objective lens in an optical pickup that is obtained by combining a plurality of lenses; the objective lens is configured so that a mark indicative of a die cavity used for molding the lens is provided in a lens to be positioned on the lower side, and the mark of the lens can be seen through a smooth part provided in a lens positioned on the upper side, above the lens on the lower side.
Patent Document 1: JP 2002-71909 A
Patent Document 2: JP 2004-205823 A